Pregnant rats were given intraperitoneal injections containing various concentrations of fluoride and 45Ca. Pups from these dams or pups injected similarly when they were 5, 9, or 12-30 days of age were sacrificed just prior to eruption of the first molars and their jaws were resected and teeth examined for radioactivity. A group of rat pups treated in the same manner using non-radioactive Ca were used to study the development of dental caries. In addition, a Ca blocking agent was used on one group of rats.